When the great B.B. King bent a nasty blues note on his guitar, it looked like someone was twisting his leg off.

There is a nebulous place where music collides with emotion, and for many musicians, this meeting of the mind’s sensory neurons, motor function, and cognition proves combustible, and whatever wells up is commonly manifested in a musician’s most noticeable feature: their face. Etta James, Neil Young, and Eddie Vedder all prove the case, and on Saturday Night Live this past weekend, Este Haim of the pop band Haim gave a truly impressive facial performance, alternating between grimaces and unfettered, wide-mouthed bewilderment. However neuro-complex the phenomenon may be, it’s likely rooted in our evolutionary past.

“Music in its history – the big, long history – never focused exclusively on the auditory component,” says Bill Thompson, who researches music and emotion at Macquarie University.

Millennia before the invention of the gramophone, back when music was never recorded and was always a live, intentional event, “music traditionally involved seeing and hearing and moving,” says Thompson.

Whether in the bowels of European cave or inside a raucous medieval tavern, music was wedded to expression, so it’s logical that our emotions are still inherently linked to our behaviors and actions.

“People are compelled by their own emotional response to their music, and that emotion is going to affect you much more than if you’re just merely listening,” Thompson says.

When one is performing, perhaps on a historic stage in front of a national audience — like Este Haim Saturday night — “it becomes a much more intense musical experience that will affect movement and facial expressions,” he says.

Darwin devoted six pages to human music in The Descent of Man, where he described an evolutionary basis for the human propensity for song, specifically as a courtship display to attract mates. 150 years later, The Rolling Stones’ Mick Jagger might agree, but modern neuroscientists think that music serves as much more than a wooing technique.

In the present day, we know that music powerfully activates our motor cortex – the part of the brain responsible for every movement we make – as we move our fingers, limbs, and mouths. Taken with a strong dose of emotional response to a meaningful tune, “this motor activity in the brain permeates your behavior and has kind of a cascade effect,” says Thompson. It’s little surprise, then, that Este Haim, while playing bass and singing her own music, is involuntarily overcome by the experience, and in her own, distinctive way, expresses it in seemingly exaggerated, though involuntarily facial expressions.

And this is precisely what we, the viewers, want to experience. “People flood to concerts, and they don’t want to close their eyes,” says Thompson. “They want to see how music affects the performer.”

Photos via Getty Images / Christopher Polk